This invention relates to a method of bonding at least two aluminum members and to a machine for practicing such method.
In the electrical apparatus field the use of aluminum strip material to form coils has become widely used throughout the industry. In the manufacture of coils, it is necessary to attach terminal and lead members to one or more portions of the aluminum strip. Where such terminals are aluminum material, it is necessary to provide a strong electrical joint between the aluminum members.
In general, the bonding of one aluminum member to another by resistance welding has been found unsatisfactory. The inability to obtain a consistently strong, uniform joint of good electrical characteristics has been often noted during the welding of aluminum to aluminum.
One method that has been used successfully is disclosed in U.S. Pat. No. 3,592,993, in the name of one of the inventors herein. However, that method requires the addition of a copper or copper alloy screen between the members to be joined. It is considered desirable to provide a method of resistance welding which does not require the use of any additional material to the joint.
It has been found that a consistently strong, electricallysound joint can be made between an aluminum lead and an aluminum winding by using hard, high-electrical resistance electrodes and relying on the oxide coating of the aluminum to provide resistance heating to spot weld the aluminum members together.
Therefore, it is one object of this invention to provide a novel method of joining aluminum to aluminum. It is a further object of this invention to provide a novel method of joining aluminum members which does not require cleaning of the aluminum surfaces, but relies on the aluminum oxide coating to provide resistance heating to aid in welding the aluminum members.
A still further object of this invention is to provide a novel machine for thermal resistance welding of aluminum members.